Objectives of this research are to understand the interactions between type 1 and 2 alveolar lining epithelium as regards their non-respiratory functions in lung. The study depends on in vitro aggregation of monodispersed lung cells from heterogenous lung cell populations and from gradients of monodispersed lung cells enriched with regard to specific cell type (e.g. type 1 or type 2 cells). Methods are aimed at aggregating type 2 and type 1 cells separately and together utilizing conditioned media, hormones, various steroids and polyamines. The structure of cell aggregates (cysts) will be studied by electron microscopy so as to establish identity with in situ cell equivalents. Cyst function will be studied by means of high resolution autoradiography and biochemical methods for saturated and disaturated phospholipids and protein. Other studies concern the role of the surface of types 1 and 2 epithelium in cell-cell interactions including cell-cell communication, possible reciprocal effects on structure and integrity and on molecular synthesis as well as aging. Of special interest to this study is the apparent alteration of cyst type 2 cells to type 1 epithelium permitting study of the transport activity of the latter.